Oscar martienssen



Patented Feb. 3, 1925.

UNITED STATES OSCAR MARTIENSSEN, 0F KIEL, GERMANY.

GAS INDICATOR.

Application filed May 15,

To all whom t may concern.'

Be it known that I` OSCAR MAnTmNssnN, citizen of the German Republic, and resid-A ing at Kiel, county of Schleswig-Holstein, State of Prussia, have invented certain new and useful Improvements in Gas Indicators, of which the following is a specification.

This invention relates in general to gas indicators and more particularly to liredamp or methane indicators in which a body that has been previously heated`r preferably by electricity, and which acts as a catalyzer and glows when brought into certain gas mixtures. The intensity with which the body glows is an approximate indication of the amount of methane contained in the air.

It is well known that certain metals such as platinum, palladium and other substances are capable of occluding light gases such as hydrogen or methane. lVhen these metals take in these gases the volume of the latter is greatly reduced so that their absorption is accompanied by a generation of heat and consequently a heating of the occluding body. lVhen the latter is saturated with gas no further generation of heat takes place. The heat generated is given off to, the surroundings of the body and the temperature of the latter again drops to that of its environment. Tf, for example`r `a platinum wire is introduced .into pure hydrogen, a brief generation of heat will take place, but only a short time elapses before the wire regains the temperature of its environment. It must be observed that this well known phenomenon is distinct from the heating process in which combustion of the occluded gases occurs when they are combined with oxygen; for if the occluding body is preheated to the temperature of ignition of the gases and suicient oxygen is enabled to come into contact with the wire the gases occluded in the surface of 'the body will burn in combining with the oxygen surrounding it and this will give rise to the production of heat. As fresh combustible gas continues to llow to the cccluding body and is burnt on the surface of the latter, the temperature of the body will be continually raised. This continual heating can, of course never take place in a pure combustible gas, but only in a mix* ture of a combustible gas and oxygen or air. The combustion will be most intensive and the temperature of the wire the great`- 1924. Serial N0. 713,470.

est when the gas mixture is such that a complete chemical conversion of the 0ccluded gas takes place.

It hasl been found that this combination of the occluded gas takes place at a temperature at which the gas b itself in normal conditions does not ignite or, in other words, does not burn with a visible llame. If a suitable catalyzer is used, the tempera ture at which the combustion commences is even lower than the temperature which gives rise to a visible incandescence of the wire.

Tf for example a pure platinum wire is used as a catalyzer and hydrogen is mixed with the surrounding air, a combustion of the hydrogen on the wire commences at a temperature of 2500 C. rlhis is to be accounted for by the great compression of the hydrogen in the wire and the reduction ofA the temperature of combustion caused thereby. ln the case of methane the conditions are much more unfavorable than with hydrogen partly because methane is not occluded to the same extent and is therefore not subjected to so great a compression in the wire, and partly because the temperature of ignition of methane is higher than that of hydrogen in any case. It has however been found by experiment that `the catalytic body can also be made highly sensitive to methane by preparing in a certain way. This preparation consists in depositing certain rare metals of the platinum of palladium group on the wire and by making the form or structure of the deposit particularly effective by applying it in porous form. It has been found that the deposit is most favorable when itis produced by evaporating a drop of a salt solution of the rare metal on the catalytic body which may have the form of a glowing wire. To enable the occluding body to be preheated in a convenient manner it is preferably made in the form of a thin wire or JEine ribbon so as to make its surface as large as possible as compared to its cross section. The preheating is accomplished best by an electric current.

When the current is regulated so that the glowing of the wire is hardly perceptible in pure air it will be found that a platiuni wire placed in air mixed with hydrogen or with a mixture of hydrogen and methane of only7 one to 2%, will be heated to a perceptible red glow. The glow will increase -suffocating the flame.

as the:` rrelative` proportion of combustible gases to the air increases, and when the ad-. mixture is 1013i the wire will glow at white heat.

If, however. such a heated pure platinum wire is exposed to an admixture o't air and methane only, no change will occur so tar as temperature ot' the wire is concerned. Only when the wire is prepared in the above described manner, namely when certain kinds or porous metals are aflixed at a number of points, the wire will assume in an airmethanc mixture the same characteristics as a pure platinum wire will assume in an airhydrogen mixture. If, for example, a loop of' platinum wire is prepared as descriled at it-screst -and then preheated by an electric current so thatthe crest is invisible in pure air, but its limbs are just perceptible, it will be found that mixtures of methane and air will cause the crest to glow much brighter than the limbs of the loop.

This peculiar behavior' of a prepared wire in methane may be explained as follows: The deposit of rare metal on the wire effects a partial decomposition of the methane and the liberated hydrogen is intensively absoi-bedy by the neighboring parts of the wire andr this hydrogen then burns in the wire with the surrounding oxygen and heats the wire. If this heating of the wire is great enouelna combustion of the carbon separated from the methane will follow and smallllames seem to form at the wire which cause it to become incandescent with a white glow at these points.

Of'course'the lWire which is thus caused to glow must not be enclosed in a totally closed chamber vas in an ordinary electric glow lamp, 'but the external. air must be allor-:ed to pass freely to the wire. On the other hand precautions are necessary to prevent the glowing wire from elliecting an ignition of the fire-damp outside oit the apparatus. This is accomplished by placing the wire in a smalllchamber whose walls partly consist of very ervious stones or so-called filter stones. uch stones have exceedingly fine` passages which, although they allow gases to pass through them, will never permit a. flame to pass through on account of the low conductivity of the stone. Hence the stones act like the wire net of' a Davy7 safety lamp, but they are also effective in other ways: for it the gas mixture is caused to flare in the combustion chamber the flames cannot continue but must immediately go out again because the gases of combustion, viz thecarbonic acid gas and steam, cannot flow out through the porous stone quickly enough to prevent them from immediately Hence a continuous flame cannotl arise -in a combustion chamber yof this kind as in a Davy safety lamp and therefore the walls .of the combustion chamber cannot be heated so as to transfer the combustion from the chamber to the external lll.

On the other hand however such stones `a re sufliciently pervious to gas to prevent any explosion in the chamber because an explosion of a gas mixture can take place when an increase of pressure arises when the gas is ignited. On account ot' the great perviousness of the stones a rise ot' pressure is however not possible and the consequence is that no sudden flaring of the entire contents ol the chamber that would give rise to an explosion takes place, but the contents of the chamber gradually burn out. It, for example, the apparatus is used in air containing hydrogen, the-n as soon as .the amount of hydrogen reaches 10%, a liame will Yform in the combustion chamber at the wire that glows at a white heat. This flame soon drops in the combustion chamber and goes out. At the same time the wire also extinguishes on account of the steam fpre venting a further penetration of' hydrogen into the wire. Hydrogen will only commence penetrating into the wire shortly aft'ter the steam has passed out, whereupon the wire is again heated to a white incandesrence by the combination of the hydrogen with the surrounding oxygen. It is t-hus seen that a flame is formed at intervals of about half a minute without any danger off gases outside the apparatus being ignited. lf the admixture in the air is not hydrogen, but methane, andthe wire is prepared in the atoredescribed manner, no flaring up of the methane mixture will as a rule occur at all because the carbonio acid gas developed at the wire prevents the combustion from spreading through the Whole chamber.

The temperatures at which the combustion particularly of methane, occurs are `very considerable and precautionary measures arc therefore necessary to prevent the catalytic body t'rom melting. This is accomplished in accordance with the present invention by .making the wire of an alloy ot' platinum and a high melting point metal of the palladiunrgroup, for instance osmium or ruthe` nium. Such a platinum alloy has besides the advantage that the catalytic effect.. of the wire matcriall)7 increased. But in spite ot the high melting points of these alloys it'urther precautions are necessary to avoid the melting of the wire. These consist in using a wire oit suitable thickness. It the wire is veryv thin the effect is greatest, butthe heat generated in a. ln'eparcd wire at the luminous portions is so intensive lthat thewirc would melt at these points. llhen the wire is made thicker it conducts the heat away from the heated parts and distributes it over a larger portion of" the wire and thus reduces the temperature. l have Jfound that with a wire of a diameter of .06 to .08 mms, the

lad

heating ettect is still sutliciently intensive while on the other hand the heat conductance is sufficient to prevent melting of the wire under all normal conditions.

Having described the essential features of the invention I will now explain a lire-damp indicator in accordance with the invention with reference to the accompanying drawing which shows an indicator partly in vertical section so as to disclose the internal arrangement. ln the drawing G is a. glass vessel containing a wire W made in the form of an ordinary lamp lilament except that the glass container is perforated as at P and a wire which has a strong catalytic etlect is employed, this wire being made of a platinum alloy of the above described character and prepared at a suitable number ot points along its length in the manner herein before described.

The glow lamp G is titted in the usual manner in a socket H through which current is conducted to its wire.

The glow lamp is placed in a chamber formed or' a cylindrical glass wall M closed at the top and bot-tom by very porous stones S and S. Placed between the stones and the glass cylinder are packing rings D ot asbestos. The parts M and S, S are held together by a metal mantle F perforated at the middle, the perfor-ations serving as observation openings through which the glow wire can be observed. The lower stone .S rests on a ring Z which forms a part of a base B which enables the gas mixture to enter the combustion chamber from below through holes C in the outer casing E in the direction indicated by the arrows. The glow wire receives current from a battery I placed in the bottom compartment U of the apparatus. Inserted in the circuit between the battery and the glow wire is a resistance R whose electrical value is such that the current from the battery heats the wire to an extent at which it is still invisible or only has a dull red glow. A regulating' switch K is provided by which the resistance can be reduced to .increase the current suiiciently to cause the unprepared portion of the wire to `low dull red when in pure air, when the prepared parts of the wire will remain darker on account of the greater cooling surtace at these parts.

Vhen the apparatus is brought into a place in which the air contains a few percent of methane, the prepared parts of the glow wire which were previously invisible brighten up to a red hue. It the content of methane is between 4 and 8%, the not prepared parts oit' the wire will become white hotwhile the prepared parts remain red. But if the content of methane is more than 8% the prepared parts will remain red hot even it' the current is switched completely ol".

The resistance Rin the circuit of the glow wire. is important for other reasons; for when the wire commences glowing its resistance increases and it' no outside resistance were in its circuit the current strength would drop and the illuminating power of the wire would be weakened. But if suftcient outside resistance is connected in the circuit, the current in the glow wire will not drop alipreciably when its resistance increasese so that its brightness will not be affected.

llt 't'ollows that by selecting a suitable resistance R and a suitable length ot the glow wire tor a given voltage ot the battery the relations ot the parts may be such that excessive heating and consequent melting of the glow wire is prevented.

I claim l. Apparatus for indicating admixtures ot combustible gases and air, in particular re damp, comprising an elongated gas absorbing body of catalytic character having a number ot' prepared portions distributed over its length, said portions consisting of precious nietal deposits of the platinumpalladium groups in porous form, means for electrically heating'said body to an extent at which the not prepared portions glow just visibly when exposed to pure air, the extent of the admixture of said gases to the air being indicated by increasing brightness o't' said glow with increasing gas percentage, the light intensity being a measure t'or the gas percentage.

Apparatus for indicating admixtures ot combustible gases and air, in particular fire damp, comprising an elongated gas absorbing body ot' an alloy of platinum and a rare metal having a melting point higher than that of platinum, said body having a number of prepared portions distributed over its length7 said portions consisting oi' precious metal deposits ot' the platinumpalladium groups in porous form, means tor electrically heating said body to an cxtent at which the not prepared portions glow just visibly when exposed to pure air, the extent of the admixture of said gases to the air being' indicated by increasing brightness of said glow with increasing gas percentage, the light intensity being a measure tor the gas percentage.

3. A tire damp indicator having an elongated catalytic body having deposited thereon at a number oit points along its length a salt ot a metal of the platinumpalladium groups, the deposit having been made when said body was suiiiciently heated so that the deposit was reduced to the form ot pure porous metal, means tor heating said body to an extent at which the not prepared portions glow just, visibly when exposed to pure air. the extent of the admixture of .said gases to the air being indicated by increasing brightness of said glow 'with increasing gas percentage, the light .intensity being a measure forl the gas percentage.

4. A fire damp indicator having a catalytic Wire of .()6-.08 111.111. in diameter, and composed of an alloy of platinum and a rare metalhaving a melting point higher' than that of platinum, said' wire having deposited thereon at a number of points along its length a salt of a metal o't the platinumpalladium groups the deposit having been made when it was suiieiently heated to redu'ee the deposit to a pure metal of porous form, means for heating said Wire to an extentat which thernot preparedvvportions 15 glow first visibly when exposed to pure air, the extent of the admiXture of gas to the air being indicated byiinoreasing brightness of said glow, with increasing gas percentage, the light intensity being a measure for the 20 gas percentage.

AIn testimony whereof I affix my signature in presence of two. witnesses.

OSCAR MARTIENSSEN.

litnesses ll. KAsPARnH7 M. BLUNGK. 

